Fertilizers have been used for some time to provide nitrogen to the soil. Commercial fertilizers can come in a variety of liquid or solid forms. The most widely used and agriculturally important liquid form of nitrogen fertilizer is urea ammonium nitrate (UAN), and the most widely used and agriculturally important solid form is granular urea, a white crystalline solid under normal conditions. Urea is a commonly used nitrogen fertilizer due to its relatively low cost and its high nitrogen concentration (46%). Solid forms of urea include granular, prilled, pelletized, powdered or dust. Normally, the granular form is somewhat larger in particle size than the prills. Most of the urea-based fertilizer currently used is produced in its granular form.
After urea is applied to soil, it is hydrolyzed to yield ammonia and carbon dioxide. This process is catalyzed by the enzyme urease, which is an extracellular enzyme in the soil. The gaseous products formed by the hydrolysis reaction (ammonia and carbon dioxide) volatilize to the atmosphere, and thus, substantial losses from the total amount of the nitrogen applied to the field occur. Accordingly, some solid, water-soluble fertilizers can be made slow-release by various additives. For example, the hydrolysis process can be considerably decelerated by applying enzyme inhibitors, specifically urease or nitrification inhibitors with urea. Examples of urease inhibitors are the thiophosphoric triamide compounds disclosed in the U.S. Pat. No. 4,530,714, including N-(n-butyl)thiophosphoric triamide (NBPT). NBPT is used in a number of agricultural products, such as AGROTAIN® and AGROTAIN® ULTRA (see, e.g., U.S. Pat. No. 5,698,003); SUPER N® (see, e.g., U.S. Pat. No. 5,364,438); and SUPER U®, UFLEXX® and UMAXX® (see, e.g., U.S. Pat. No. 5,352,265).
Examples of nitrification inhibitors include, but are not limited to, dicyandiamide (DCD), nitrapyrin and 3,4-dimethylpyrazole phosphate (DMPP). DCD can be a difficult material to handle as it has poor solubility in most solvents. Accordingly, there remains a need for new compositions and methods of improving the properties of urea-based fertilizers coated with nitrification inhibitors. The present invention as described herein addresses this and other needs by providing a formulation of DMPP, nitrapyrin, or other nitrification inhibitors with a urea-formaldehyde polymer (e.g., as disclosed in U.S. Pat. No. 6,936,681). The formulation of the present invention significantly lowers the use rates of nitrification inhibitors in agricultural applications.